Name: chemical equilibrium and kc rules
Uploaded: 2025-08-11T09:37:07.000Z
Duration: 3 min 10 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.5.2

The Equilibrium Constant

Kütle etkisi yasası, reaktanların ve ürünlerin denge konsantrasyonlarını ilişkilendirmek için denge sabitini ileri sürer. A ve B'nin reaktan, C ve D'nin ürünler olduğu ve küçük harfli a, b, c ve d'nin onların stokiyometrik katsayıları olduğu dengeli bir kimyasal denklem için, denge sabiti ifadesi, ürünlerin molar konsantrasyonlarının reaktanların molar konsantrasyonlarına bölünmesiyle elde edilit, ve bunların hepsinin stokiyometrik katsayıları alınmıştır. Denge sabiti genellikle K veya Kc sembolü ile ifade edilir, burada alt simge c molar konsantrasyona göre denge sabitini gösterir.Molar konsantrasyonların bir oranı olan denge sabiti birimsizdir. 1'den çok daha büyük olan bir denge sabiti, payın, yani ürünlerin konsantrasyonunun, paydadan, yani reaktanların konsantrasyonundan daha büyük olduğu anlamına gelir. Bu, dengenin ürünlere doğru uzandığını ve ileri reaksiyonu desteklediğini gösterir.Tersi olarak, 1'den çok daha küçük olan bir denge sabiti, paydanın paydan daha büyük olduğu anlamına gelir Bu, dengenin reaktanlara doğru olduğunu ve ters reaksiyonu desteklediğini gösterir. 1'e eşit veya 1'e yakın büyüklükteki bir denge sabiti için, reaktanların ve ürünlerin nispi konsantrasyonları hemen hemen aynıdır. Bu, ne ileri ne de geri tepkimenin tercih edilmediğini gösterir.Kimyasal denklemde yapılan değişiklikler de denge sabitini değiştirir. Denge sabiti x olan bir kimyasal reaksiyon tersine çevrilirse, ters reaksiyon için denge sabiti ifadesi ileri reaksiyonun tersidir. Yani, yeni denge sabiti 1 bölü x olacaktır.Katsayılar başka bir faktörle çarpılırsa, denge sabiti aynı faktöre yükseltilir. Yeni denge sabiti x, şimdi n kuvvetine yükseltilecektir. İki veya daha fazla tekil reaksiyon birlikte eklendiğinde, genel reaksiyon için denge sabiti, ayrı ayrı denge sabitlerinin ürünüdür.Yani, yeni denge sabiti y çarpı z olacaktır. Heterojen bir denge için, denge sabiti ifadesi, saf katı veya saf sıvı varlıkları hariç tutar. Örneğin, katı amonyum nitratın gaz halindeki nitröz okside ve su buharına ayrışması için denge sabiti ifadesi, saf bir katı olan amonyum nitratı hariç tutar.Bunun nedeni, saf bir katı veya sıvının nispi molar konsantrasyonunun reaksiyon sırasında sabit kalmasıdır.

denge sabiti

Kükürt dioksitin oksidasyonunu düşünün:
 
 <img alt=""Eq1"" src=""/files/ftp_upload/11386/11386_Equation_1.png"" style=""text-align: center; height: 50px;"" />
 
 Yalnızca reaktanların bir karışımıyla başlayan bir reaksiyon için, ürün konsantrasyonu başlangıçta sıfıra eşittir. Reaksiyon ileri yönde dengeye doğru ilerlerken, reaktan konsantrasyonları azalır ve ürün konsantrasyonu artar. Denge sağlandığında, reaktanların ve ürünlerin konsantrasyonları sabit kalır.
 
 Reaksiyon sadece mevcut ürünlerle başlarsa, reaksiyon ters yönde dengeye doğru ilerler. Ürün konsantrasyonu zamanla azalır ve dengede konsantrasyonlar sabit hale gelene kadar reaktan konsantrasyonları artar.
 
 Kütle etkisi yasası, ürün konsantrasyonunun, ilgili stokiyometrik katsayılarına yükseltilen dengede reaktanların konsantrasyonuna oranının, denge sabiti K ya da Kc denilen bir sabite eşit olduğunu belirtir.
 
 Bu nedenle, yukarıdaki reaksiyon için denge sabiti ifadesi şu şekilde yazılır:
 
 <img alt=""Eq2"" src=""/files/ftp_upload/11386/11386_Equation_2.png"" style=""text-align: center; height: 100px;"" />
 
 burada, ‘c’ alt simgesi, denge sabitinin, reaktanların ve ürünlerin molar konsantrasyonunu dikkate aldığını belirtir.
 
 Denge sabitinin büyüklüğü, açıkça dengede bir reaksiyon karışımının bileşimini yansıtır. Büyük bir K sergileyen bir reaksiyon, reaktanın çoğu ürüne dönüştürüldüğünde dengeye ulaşacaktır, oysa küçük bir K , reaksiyonun çok az reaktan dönüştürüldükten sonra dengeye ulaştığını gösterir. K 'nin büyüklüğünün dengeye ne kadar hızlı veya yavaş ulaşılacağını göstermediğini unutmamak önemlidir. Bazı dengeler o kadar hızlı kurulur ki neredeyse anlık olur ve diğerleri o kadar yavaş kurulur ki günler, yıllar veya daha uzun süre boyunca hiçbir algılanabilir değişiklik gözlenmez. Bir reaksiyon için denge sabiti, reaktanlarını ve / veya ürünlerini içeren karışımların davranışını tahmin etmek için kullanılabilir. Yukarıda açıklanan kükürt dioksit oksidasyon işleminin gösterdiği gibi, dengeyi sağlamak için gereken yönde kimyasal bir reaksiyon ilerleyecektir.
 
 Birleştirilmiş Denge
 
 Birçok denge sistemi, ortak olarak bir veya daha fazla reaktan veya ürün türüne sahip olan iki veya daha fazla  birleştirilmiş  denge reaksiyonu içerir. Birleştirilmiş dengeleri içeren bir sistem için  K  değeri, tek tek reaksiyonların  K  değerleriyle ilişkili olabilir. Aşağıda açıklandığı gibi, bu yaklaşımda üç temel manipülasyon söz konusudur: 
 
 • Bir kimyasal denklemin yönünü değiştirmek, esasen “reaktanlar” ve “ürünlerin” kimliklerini değiştirir ve bu nedenle tersine çevrilmiş denklem için denge sabiti, ileri denklem için olanın basitçe tersidir. 
 
 •  Bir denklemdeki stokiyometrik katsayıların, bir faktör  x  ile değiştirilmesi, aynı faktör kadar denge sabitinde üstel bir değişikliğe neden olur. 
 
 •  İki veya daha fazla denge denkleminin toplanması, denge sabiti reaksiyonun  K  değerlerinin matematiksel ürünü olan genel bir denklem verir.
 
 Heterojen Denge için Denge Sabiti İfadesi
 
 İki veya daha fazla farklı fazdaki reaktanları ve ürünleri içeren heterojen denge için, aşağıdaki örnekte gösterildiği gibi, saf katıların veya saf sıvıların konsantrasyonları denge sabiti ifadesine dahil edilmez:
 
 <img alt=""Eq3"" src=""/files/ftp_upload/11386/11386_Equation_3.png"" style=""text-align: center; height: 150px;"" />
 
 Bunun nedeni, saf sıvılar ve saf katılar için bağıl konsantrasyonların reaksiyon sırasında sabit kalmasıdır.
 
 Bu metin bu kaynaktan uyarlanmıştır: <a href=""https://openstax.org/books/chemistry-2e/pages/13-2-equilibrium-constants"">Openstax, Chemistry 2e, Section 13.2 Equilibrium Constants</a>.

Denge Sabiti

Kükürt dioksitin oksidasyonunu düşünün:

Yalnızca bir reaktan karışımı ile başlayan bir reaksiyon için, ürün konsantrasyonu başlangıçta ...

Education

JoVE Core

Kimya

Chemical Equilibrium

Kimyasal Denge

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

chemical equilibrium and kc rules

Chemical equilibrium and the equilibrium constant Kc describe how reactants and products are balanced in a reaction. In the oxidation of sulfur dioxide, a mixture that starts with reactants only has no product at first. As the reaction moves forward toward equilibrium, reactant concentrations decrease and product concentration increases. When equilibrium is reached, the concentrations of both stay constant.

A reaction can also begin with only products present. In that case, the reaction moves in reverse toward equilibrium. The product concentration falls with time, and the reactant concentrations rise until both become constant. This shows that a chemical reaction will move in whatever direction is needed to reach equilibrium.

The law of mass action links equilibrium to a constant value. It states that the ratio of product concentrations to reactant concentrations, each raised to their stoichiometric coefficients, equals the equilibrium constant, K or Kc. The subscript c means the expression uses molar concentration. The size of K shows the mixture makeup at equilibrium. A large K means most reactant has changed to product before equilibrium is reached. A small K means only a little reactant changes to product. The value of K does not tell how fast equilibrium is reached.

Some equilibria form very quickly. Others take so long that no visible change may be seen for days, years, or longer. The equilibrium constant can still be used to predict how a mixture with reactants and/or products will behave. For coupled equilibria, two or more equilibrium reactions share one or more species. The K value for the overall system can be found from the K values of the separate reactions. Reversing a chemical equation changes K to its reciprocal. Multiplying the stoichiometric coefficients by a factor x changes K by that same factor as an exponent. Adding equilibrium equations gives an overall K equal to the product of the individual K values.

For heterogeneous equilibria, the reactants and products are in different phases. Pure solids and pure liquids are not included in the equilibrium constant expression. Their concentrations stay constant during the reaction, so they do not change the value of K. This rule is an important part of writing equilibrium expressions correctly.

Chemical Equilibrium and Kc Rules

the equilibrium constant

Chemical equilibrium and the equilibrium constant Kc describe how reactants and products are balanced in a reaction. In the oxidation of sulfur dioxide, a mixture that starts with reactants only has no product at first. As the reaction moves forward toward equilibrium, reactant concentrations decrease and product concentration increases. When equilibrium is reached, the concentrations of both stay constant. A reaction can also begin with only products present. In that case, the reaction moves...

homogeneous equilibria for gaseous reactions

homogeneous-equilibria-for-gaseous-reactions

Relating Kc and Kp in Gas Equilibria

Gas-phase equilibrium can be written using either concentration or pressure. The equilibrium constant may be shown as Kc, which uses molar concentration, or as Kp, which uses partial pressure of the reactants and products. The link between Kc and Kp comes from the ideal gas equation and the definition of molarity. Molarity is the number of moles divided by volume. In the ideal gas equation, P stands for partial pressure, V for volume, n for number of moles, R for the gas constant, and T for...

le chatelier's principle: changing concentration

le-chatelier-s-principle-changing-concentration

Shifting Equilibrium by Changing Concentration

Chemical equilibrium is a dynamic balance. At equilibrium, the forward and reverse reactions happen at equal rates. If the system is stressed in a way that changes one rate more than the other, it is no longer at equilibrium and will shift until balance is restored. This behavior is described by Le Châtelier’s principle. Changes in concentration are a major stress on an equilibrium system. Reaction rates depend mainly on concentration and temperature. For that reason, changing the amount of a...

calculating the equilibrium constant

Finding Kc from Equilibrium Data

The equilibrium constant, Kc, can be found from the equilibrium concentrations of reactants and products. When those concentrations are known, the calculation is straightforward. The values are placed into the Kc expression for the reaction. One example uses nitrogen dioxide and dinitrogen tetroxide. When 0.10 mol NO2 is added to a 1.0-L flask at 25 °C, the concentrations change until equilibrium is reached. At equilibrium, [NO2] is 0.016 M and [N2O4] is 0.042 M, and these values are used to...

reaction quotient

Using Q to Track Equilibrium Changes

Reaction quotient Q helps track how far a reversible reaction has moved toward equilibrium. For a balanced reaction such as m A + n B ⇌ x C + y D, Q comes directly from the stoichiometric coefficients in the equation. When concentrations are used, the expression is written as Qc. For gases, a similar form uses partial pressures. These expressions use relative concentration and pressure values, not absolute values. That means reaction quotients are dimensionless and have no units. As a reaction...

dynamic equilibrium

Chemical Equilibrium in Reversible Reactions

Chemical equilibrium in reversible reactions happens when a reaction moves in both directions at the same time. A reversible reaction uses a double arrow to show that products can turn back into reactants. At equilibrium, the concentrations of reactants and products stay constant over time because the forward and reverse reaction rates are equal. The video uses the reversible decomposition of colorless dinitrogen tetroxide to brown nitrogen dioxide as an example. At time zero, there is finite...

calculating equilibrium concentrations

Equilibrium Concentrations from an ICE Table

Equilibrium concentrations can be found from initial concentrations and an equilibrium constant. This skill matters in many areas of science and technology, including pharmaceutical product formulation and dosing. After a drug is ingested or injected, it may take part in several chemical equilibria that change its final concentration in the body system of interest. Scientists use these quantitative equilibrium relationships to help calculate a dosage that will produce the desired therapeutic...

le chatelier's principle: changing volume (pressure)

le-chatelier-s-principle-changing-volume-pressure

Gas Equilibrium Under Volume Changes

Gas-phase equilibrium can shift when the volume of the system changes. In these reactions, a change in pressure changes concentration because the partial pressure of an ideal gas is proportional to its molar concentration. That means pressure changes affect equilibrium in the same way as concentration changes. When the volume of a gas mixture changes, the concentrations of reactants and products change together. Since every gas in the equilibrium occupies the same space, the same volume change...

le chatelier's principle: changing temperature

le-chatelier-s-principle-changing-temperature

Le Chatelier's Principle in Heating and Cooling

Le Chatelier's principle helps explain how chemical equilibrium responds to heating and cooling. A system at equilibrium will shift to restore balance after a temperature change, but the equilibrium constant, K, will not stay the same. Instead, the mixture reaches a new equilibrium with a different composition. This temperature effect is different from a concentration change, which shifts equilibrium without changing K. To understand why temperature matters, the reaction can be written with...

the small x assumption

Estimating Equilibrium with Small Changes

A small equilibrium constant can make equilibrium calculations easier. In these reactions, the equilibrium position favors the reactants. When the initial reactant concentration is high and the Kc value is small, the change in concentration may be negligible. In that case, the equilibrium concentration is close to the initial concentration. This idea helps simplify weak acid and weak base problems. Chemists can assume that some equilibrium concentrations are equal to the initial concentrations.

key terms and concepts

Explore chemical equilibrium, Kc, and the law of mass action. Learn how concentration changes, reaction direction, and mixed-phase equilibria shape equilibrium expressions.

Chemical Equilibrium and Kc Rules | JoVE K12

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Pennsylvania State Academic Standards

Physical Science

Chemical Reactions

3.2.9-12.F

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Arizona Science Standards

High School

HS+C.P1

HS+C.P1U1.6

Next Generation Science Standards

Matter and Its Interactions

HS-PS1-6

Florida Department of Education

SC.912.P.12

SC.912.P.12.13

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South Carolina College and Career Ready Science Standards

C-PS1-6

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-6.

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Chemical Equilibrium and Kc Rules

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